8.2 decks, pools, and accessory structures

Key Issuesn Any deck, accessory building, or

other construction element that is structurally dependent on or attached to a building in V Zone is considered part of the build-ing and must meet the NFIP reg-ulatory requirements for con-struction in V Zone (see NFIP Technical Bulletin 5-08 and Fact Sheet Nos. 1.2, 1.4, 1.5, 1.7, 3.1, 8.1, 9.1). Attached con-struction elements that do not meet these requirements are prohibited.

n If prohibited elements are at-tached to a building that is oth-erwise compliant with NFIP requirements, a higher flood in-surance premium may be as-sessed against the entire building.

n Swimming pools, accessory build-ings, and other construction elements outside the perimeter (footprint) of, and not attached to, a coastal building may alter the characteris-tics of flooding significantly or increase wave or debris impact forces affecting the building and nearby buildings. If such elements are to be con-structed, a design professional should consider their potential effects on the building and nearby buildings.

n This Home Builder’s Guide to Coastal Construction strongly recommends that all decks, pools, ac-cessory structures, and other construction ele-ments in Zone A in coastal areas be designed and constructed to meet the NFIP V Zone re-quirements.

n Post-storm investigations frequently reveal enve-lope and structural damage (to elevated build-ings) initiated by failure of a deck due to flood

and/or wind forces. Decks should be given the same level of design and construction attention as the main building, and failure to do so could lead to severe building damage.

DecksRequirementsn If a deck is structurally attached to a building in

Zone V, the bottom of the lowest horizontal mem-ber of the deck must be elevated to or above the elevation of the bottom of the building’s lowest horizontal member.

n A deck built below the Design Flood Elevation (DFE) must be structurally independent of the main building and must not cause an obstruction.

n If an at-grade, structurally independent deck is to be constructed, a design professional must

Purpose: To summarize National Flood Insurance Program (NFIP) requirements and general guidelines for the construction and installation of decks, access stairs and elevators, swimming pools, and accessory buildings under or near coastal buildings.

Damage from Hurricane Opal in Florida. This deck was designed to meet State of Florida Coastal Construction Control Line (CCCL) requirements. The house predated the CCCL and did not meet the requirements.

HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION

8.2: DECKS, POOLS, AND ACCESSORY STRUCTURES

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HOME BUILDER’S GUIDE TO COASTAL CONSTRUCTION Technical Fact Sheet No. 8.2

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Decks, Pools, and Accessory Structures

evaluate the proposed deck to determine wheth-er it will adversely affect the building and nearby buildings (e.g., by diverting flood flows or creat-ing damaging debris).

Recommendationsn Decks should be built on the same type of foun-

dation as the primary building. Decks should be structurally independent of the primary structure and designed to resist the expected wind and water forces.

n Alternatively, decks can be cantilevered from the primary structure; this technique can minimize the need for additional foundation members.

n A “breakaway deck” design is discouraged be-cause of the large debris that can result.

n A “breakaway deck” on the seaward side poses a damage hazard to the primary structure.

n Decks should be constructed of flood-resistant materials, and all fasteners should be made of corrosion-resistant materials.

Access Stairs and ElevatorsRequirementsn Open stairs and elevators attached to or be-

neath an elevated building in V Zone are ex-cluded from the NFIP breakaway wall re-quirements (see NFIP Technical Bulletin 5-08 and Fact Sheet No. 8.1), but must meet the NFIP requirement for the use of flood-resis-tant materials (see NFIP Technical Bulletin 2-08 and Fact Sheet No. 1.7). Large solid staircases that block flow under a building are a violation of NFIP free-of-obstruction requirements (see NFIP Technical Bulletin 5-08)

n Although they need not be designed to break away under flood forces, access stairs and ele-vators are obstructions; therefore, the loads they may transfer to the main building must be con-sidered by the design professional.

Recommendationsn Open stair handrails and risers should be used

because they allow wind and water to pass through rather than act as a barrier to flow.

n The bottom of the stair, like the foundation of the primary structure, should be designed and con-structed to remain in place during a windstorm or a flood.

n Stairways not considered the primary means of egress can be constructed with hinged connec-tions that allow them to be raised in the event of an impending storm or flood (check code require-ments before employing this technique).

n Elevators should be installed in accordance with the guidance in NFIP Technical Bulletin 4-93 and the building code.

Swimming PoolsRequirementsn An at-grade or elevated pool adjacent to a coast-

al building is allowed only if the pool will not act as an obstruction that will result in damage to the building or nearby buildings.

n When a pool is constructed near a building in Zone V, the design professional must assure community officials that the pool will not increase the potential for damage to the foundation or elevated portion of the building or any nearby

Large solid stairs such as these block flow under a building and are a violation of NFIP free-of-obstruction requirements.

The rails on these stairs were enclosed with siding, presenting a greater obstacle to the flow of flood wa-ter and contributing to the flood damage shown here.

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buildings. Pools can be designed to break up (“frangible pools”) during a flood event, thereby reducing the po-tential for adverse impacts on near-by buildings.

n Any pool constructed adjacent to a coastal building must be structurally independent of the building and its foundation.

n A swimming pool may be placed be-neath a coastal building only if the top of the pool and the accompany-ing pool deck or walkway are flush with the existing grade and only if the lower area (below the lowest floor) remains unenclosed. Under the NFIP, lower-area enclosures around pools constitute a recreational use and are not allowed, even if constructed to breakaway standards.

Recommendationsn Pools should be oriented with their

narrowest dimension perpendicular to the direction of flood flow.

n Concrete decks or walkways around pools should be frangible (i.e., they will break apart un-der flood forces).

n Molded fiberglass pools should be installed and elevated on a pile-supported structural frame.

n No aboveground pools should be constructed in V Zone unless they are above the DFE and have an open, wind- and flood-resistant foundation.

n Pool equipment should be located above the DFE whenever practical.

n Check with community officials before construct-ing pools in Zone V.

Accessory BuildingsRequirementsn Unless properly elevated (to or above the DFE)

on piles or columns, an accessory building in V Zone is likely to be destroyed during a coastal storm; therefore, these buildings must be lim-ited to small, low-value structures (e.g., small wood or metal sheds) that are disposable. See NFIP Technical Bulletin 5-08.

n If a community wishes to allow unelevated ac-cessory buildings, it must define “small” and “low cost.” NFIP Technical Bulletin 5-08 defines “small” as less than 100 square feet and “low cost” as less than $500. Unelevated accessory

buildings must be unfinished inside, constructed with flood-resistant materials, and used only for storage.

n When an accessory building is placed in Zone V, the design professional must determine the ef-fect that debris from the accessory building will have on nearby buildings. If the accessory build-ing is large enough that its failure could create damaging debris or divert flood flows, it must be elevated above the DFE.

Recommendationsn Whenever practical, accessory buildings should

not be constructed. Instead, the functions of an accessory building should be incorporated into the primary building.

n All accessory buildings should be located above the DFE whenever practical.

n All accessory buildings should be designed and constructed to resist the locally expected wind and water forces whenever practical.

n The roof, wall, and foundation connections in ac-cessory buildings should meet the requirements for connections in primary buildings.

n Accessory buildings below the DFE should be an-chored to resist being blown away by high winds or carried away by floodwaters.

Siting and design recommendations for swimming pools in coastal areas.



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n Accessory buildings (including their foundations) must not be attached to the primary build-ing; otherwise, failure of the ac-cessory building could damage the primary building.

n Orienting the narrowest dimen-sion of an accessory building perpendicular to the expected flow of water will create less of an obstruction to flowing water or wave action, and may result in less damage.

Additional ResourcesFEMA. NFIP Technical Bulletin 2-08, Flood Damage-Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas. (http://www.fema.gov/library/viewRecord.do?id=1580)

FEMA. NFIP Technical Bulletin 4-10, Elevator Installation for Buildings Located in Special Flood Hazard Areas. (http://www.fema.gov/library/viewRecord.do?id=1717)

FEMA. NFIP Technical Bulletin 5-08, Free-of-Obstruction Requirements for Buildings Located in Coastal High Hazard Areas. (http://www.fema.gov/library/viewRecord.do?id=1718)

Small accessory building anchored to resist wind forces.

Developed in association with the National Association of Home Builders Research Center



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http://www.fema.gov/library/viewRecord.do?id=1580



8.2 decks, pools, and accessory structures

Documents